Using a new perf tool against an older kernel

[Arun Sharma <asharma@fb.com>]

I ran into a few strange issues today using a new perf tool (3.0-rcX) 
against a 2.6.38 based kernel. Basic things seem to work:

# perf record -aR -- sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.443 MB perf.data (~19334 samples) ]

But:

# perf record -agR -- sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 1.558 MB perf.data (~68077 samples) ]
Can't find id 9's machine
Found 1 unknown events!

Is this an older tool processing a perf.data file generated by a more 
recent tool?

If that is not the case, consider reporting to linux-kernel@vger.kernel.org.

I couldn't tell if this is kernel/user space incompatibility or tighter 
error checking in the new perf tool. Before I start digging further, 
thought I'd ask if this combination is supported. The error message 
above doesn't ask me:

Are you using an old kernel?

  -Arun